Hemodialysis (HD) patients have reduced circulating levels of 1,25-OH vitamin D levels because its major site of production is the healthy kidney via the 1-alpha hydroxylase enzyme. The deficiency is treated with intravenous1,25-OH active vitamin D at dialysis which is titrated to achieve a targeted parathyroid hormone (PTH) value recommended by the National Kidney Foundation (NKF) Kidney Dialysis Outcomes Quality Initiative (KDOQI) Guidelines. Despite these intravenous vitamin D treatments, HD patients have a very high prevalence of 25-OH vitamin deficiency. 25-OH deficiency has been associated with poor neuromuscular function and cognition in non-dialysis populations. The role vitamin 25-OH D deficiency in the highly prevalent muscle weakness and cognitive impairment experienced by HD patients is currently not known. Since many tissues other than the kidney possess the 1-alpha hydroxylase enzyme capable of activating 25 OH vitamin D to 1-25 OH vitamin D, administering IV active vitamin D solely to target a PTH range may completely neglect important vitamin D on other extra-skeletal tissues. The primary goal of our study is to determine the effect of vitamin D supplementation on neuromuscular and cognitive function in HD patients with 25-OH vitamin D levels < 20 ng/ml. We propose a prospective, randomized, [double-blind placebo controlled] trial. Enrolled participants will be randomized 2:1 to receive vitamin D (n=20) or [placebo] (n=10) for 6 months. Following baseline neuromuscular and cognitive assessments, the treatment group will receive 50,000 IU of oral ergocalciferol every two weeks for 6 months, and have 25(OH) vitamin D3 levels re-measured at monthly intervals. Following 6 months of vitamin D supplementation, neuromuscular and cognitive assessments will be performed. Results from neuromuscular function and cognitive assessments between the [placebo] arm and treatment will be analyzed as well as differences in assessments prior to and following the 6 month interval in both groups.